The invention relates to the field of gas turbine engines, and more specifically, to gas turbines maintaining control of fluid density to control system operation and to minimize losses.
In conventional gas turbine engines having a turbine and a compressor, turbine output power is controlled by simply varying the fuel supply. When fuel supply is increased, the temperature upstream of the turbine increases, resulting in increased power and speed. This also causes an increase in pressure and in the expansion ratio. Controlling power in conventional gas turbine engines in this way does not pose any significant problems, but these engine are unable to accommodate sudden load changes because the temperature in the gas turbine engine changes over a very wide range: from 600xc2x0 K to 1,400xc2x0 K when operating from idling conditions to full load. In addition, it is not possible to xe2x80x9cscale downxe2x80x9d a conventional gas turbine engine to obtain a lower-power, compact engine for uses such as land vehicle applications because the turbine flow duct fluid parameters would require turbine blades to be as small as xe2x85x9 of an inch in height. With such small blades, the engine would not produce enough torque, thus requiring a gearbox and lowering overall efficiency.
These disadvantages can be partly eliminated by reducing the pressure downstream of the turbine with an exhauster. The exhauster allows the expansion ratio to be increased and the pressure upstream of the turbine to be decreased. Turbine blades can then be made larger, and consequently produce more torque than otherwise would have been possible. This does not completely solve the problem because turbine flow duct temperature fluctuations remain. Wide temperature fluctuations result in engine components incurring large thermal expansions and contractions. These deformations result in metal-to-metal clearance variations (which gives rise to losses), lower reliability, and reduced service life.
Our co-pending application Ser. No. 09/161,114 of Sep. 25, 1998 discloses a gas turbine engine having a compressor, a power turbine and is mounted downstream of the compressor, and a compressor turbine for powering the compressor. The compressor turbine is mounted downstream of the power turbine for rotation in a direction opposite to the rotation direction of said power turbine. A heated fluid source is provided upstream of the power turbine and is connected to a fuel source. The engine has a heat exchanger for cooling the waste fluid after the compressor turbine before compression of this waste fluid in the compressor and for cooling heating the waste fluid after the compressor before feeding this compressed waste fluid to the heated fluid source. To control the power of the gas turbine engine, the density of the fluid in the flow duct of the engine is controlled by removing a part of the compressed heated waste fluid leaving the heat exchanger before the compressed waste fluid is fed to the combustor. The part of the compressed heated waste fluid that is removed into the atmosphere is replaced with combustion air which is fed to the heated fluid source. A turbocompressor unit is used to remove the waste fluid and to replace it with air for combustion.
The above-described approach controls the fluid density in the engine flow duct, thus controlling engine power. The main problem with this density control method is it incurs energy losses when part of the waste fluid is removed from the flow duct into the atmosphere. As shown in the above description of the prior art, the compressed waste fluid is heated in the heat exchanger before a part of it is removed from the flow duct. This means that a part of the heat exchanger capacity is used for heating that part of the waste fluid which will then be removed into the atmosphere. When this happens, the energy that was used for heating the part of the waste fluid which is exhausted is wasted. In addition, the turbine that is used to remove the excessive waste fluid from the flow duct of the gas turbine engine works with the heated waste fluid (at about 700xc2x0 C.). The turbine used for removing the waste fluid, which is an auxiliary turbine, has to be manufactured to withstand this temperature, which requires exacting manufacturing tolerances and the use of special materials. These auxiliary turbines have a high cost and limited reliability.
Another disadvantage of the prior art is that combustion air is supplied to the combustor by an auxiliary compressor which is driven by the same auxiliary turbine that is used to remove the excessive waste fluid from the engine flow duct. This is rather ineffective, especially under transient conditions, because the auxiliary compressor capacity fully depends on the power of the auxiliary turbine, which power, in turn, is determined by the amount of the waste fluid exhausted through the auxiliary turbine into the atmosphere. The amount of the waste fluid exhausted into the atmosphere is determined by a complicated control system, and there is no direct relationship between the pressure (fluid density) in the gas turbine engine flow duct and the amount of waste fluid that is exhausted, hence the amount of combustion air which is supplied to the combustor. Because there is no direct relationship between the waste fluid removal system and the control parameters of the power turbine and of the compressor turbine and there are present substantial gas paths with high thermodynamic inertia upstream of the waste fluid removal system, the waste fluid removal and combustion air supply system respond slowly, which results in the gas turbine engine operating sluggishly under transient conditions.
The prior art system requires a special control subsystem with sensors and control elements for transition to idling. This makes the control system of the engine more complicated.
It is thus an object of the invention to avoid this complicated form of control system.
It is also an object of the invention to provide a gas turbine engine having a greater efficiency.
Another object of the invention is to provide a gas turbine engine which has a faster response over the full power range.
Further object of the invention is to provide a gas turbine engine which is simpler and more reliable in operation.
The above and other objects are accomplished by providing a gas turbine engine having a compressor unit that has two inlets and two outlets, one outlet of which communicates with the atmosphere. The gas turbine engine has a power turbine and a counter-rotating compressor turbine for powering the compressor unit. A control device controls temperature at the compressor turbine outlet. The compressor turbine outlet is connected via a heat exchanger to one inlet of the compressor unit and compresses waste fluid which is fed from one outlet of the compressor unit through a heat exchanger to a first flow control connected to one inlet of a mixer. The second inlet of the compressor unit communicates with the atmosphere. Compressed air is supplied from the second outlet of the compressor unit to a second inlet of the mixer through a second flow control. The mixer is connected to a combustor for supplying heated fluid to the power turbine and compressor turbine.
Other objects and advantages of the invention will become apparent from the following description of preferred embodiments thereof with the reference to the accompanying drawings.